Kinetics and mechanism of the hydroxylation of some naphthalene sulphonic acid derivatives by peroxodisulphate

Abstract

Oxidation of 1,8-dihydroxynaphthalene-3,6-disulphonic acid (CTA) and 1-amino-4-naphthalene sulphonic acid (ANS) by potassium peroxodisulphate leads to hydroxylation of these organic compounds. These oxidations may proceed through inner-sphere electron transfer as in case of ANS or by outer-sphere mechanism in case of CTA. The homolytic fission of S₂O₈²⁻ is the rate determining step in the oxidation of CTA by S₂O₈²⁻, whereas, the intramolecular electron transfer in the precursor compounds is the rate determining step in the mechanism of oxidation of ANS. Hydroxylation takes place in para-position of benzene ring in CTA and ortho-position in ANS. The thermodynamics activation parameters were calculated. Rate of oxidation of both CTA and ANS in methanol-water solvent mixtures is decreased by increasing methanol content in the medium.